Quantification of osteopontin in human plasma with an ELISA: basal levels in pre- and postmenopausal women.

OBJECTIVES

To develop an immunoassay for osteopontin (OPN), a secreted phosphoglycoprotein that is implicated in a number of human diseases, and establish basal plasma OPN levels in healthy women.

DESIGN AND METHODS

An antigen-capture ELISA was developed to quantity OPN in plasma using a combination of mouse monoclonal and rabbit polyclonal antibodies. Basal OPN levels were determined in blood plasma of 21 pre- and 14 postmenopausal women obtained at 7-day intervals over a 4-week period.

RESULTS

A group of 35 healthy women had a median OPN level of 31 micrograms/L (range = 14-64 micrograms/L). Comparison between pre- and postmenopausal women showed that their 4-week average OPN levels did not differ significantly (p > 0.16, Mann-Whitney test), and that levels in each premenopausal individual remained constant during the menstrual cycle, unaffected by cyclical levels of leuteinizing hormone and progesterone.

CONCLUSION

Systematic quantification of plasma OPN can now be done by ELISA, which was used to establish basal plasma OPN levels in a group of healthy women. Levels in pre- and postmenopausal women appeared relatively stable over a 4-week period.